U.S. patent application number 09/813038 was filed with the patent office on 2001-12-13 for method for joining biological tissues.
This patent application is currently assigned to Firma Biomedy AG. Invention is credited to Alexander, Reztsov, Eugeny, Karpov.
Application Number | 20010051800 09/813038 |
Document ID | / |
Family ID | 20235949 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010051800 |
Kind Code |
A1 |
Eugeny, Karpov ; et
al. |
December 13, 2001 |
Method for joining biological tissues
Abstract
A method is provided for obtaining a quality discontinuous
surgical suture of biological tissues. The method includes treating
the biological tissues with a laser beam having a power flux
density of 1-7 kW/cm.sup.2, preferably 3-5 kW/cm.sup.2, on the
surface of the joined biological tissues. To form a discontinuous
surgical suture, a laser is used which is powered by copper vapors
for generating a laser beam at a wavelength of 0.5-0.6 microns in
combination with short-focus optics. The source of laser radiation
has a radiation power of 5-15 W, preferably 8-11 W, at a periodic
pulse operating mode of laser beam generation and at a focal
distance of the focusing objective of 3-7 cm and the exposure
period of the biological tissues being treated by the laser
radiation is 3-15 seconds.
Inventors: |
Eugeny, Karpov; (Moscow,
RU) ; Alexander, Reztsov; (Moscow, RU) |
Correspondence
Address: |
ROBERT W. BECKER & ASSOCIATES
11896 N. Highway 14, Suite B
Tijeras
NM
87059
US
|
Assignee: |
Firma Biomedy AG
Alpenstrasse 14
Zug
CH
|
Family ID: |
20235949 |
Appl. No.: |
09/813038 |
Filed: |
March 19, 2001 |
Current U.S.
Class: |
606/8 |
Current CPC
Class: |
A61B 2017/00508
20130101; A61B 18/20 20130101 |
Class at
Publication: |
606/8 |
International
Class: |
A61B 018/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 13, 2000 |
RU |
2000-114 847 |
Claims
What we claim is:
1. A method of joining biological tissues comprising: treating the
biological tissues to be joined with a laser beam having a power
flux density of 1-7 kW/cm.sup.2 on the surface of the joined
biological tissues.
2. A method according to claim 1 wherein the step of treating the
biological tissues includes treating the biological tissues to be
joined with a laser beam having a power flux density of 3-5
kW/cm.sup.2 on the surface of the joined biological tissues.
3. A method according to claim 1, wherein the step of treating the
biological tissues includes treating the biological tissues with a
laser which is powered by copper vapors and generates a laser beam
at a wavelength of 0.5-0.6 microns in combination with short-focus
optics.
4. A method according to claim 1, wherein the step of treating the
biological tissues includes treating the biological tissues with a
laser having a laser radiation power of 5-15 W at a periodic pulse
operating mode of laser beam generation.
5. A method according to claim 1, wherein the step of treating the
biological tissues includes treating the biological tissues with a
laser having a laser radiation power of 8-11 W at a periodic pulse
operating mode of laser beam generation.
6. A method according to claim 1, wherein the step of treating the
biological tissues includes treating the biological tissues with a
laser beam generated at a focal distance of the focusing objective
of 3-7 cm.
7. A method according to claim 1, wherein the step of treating the
biological tissues includes treating the biological tissues with a
laser beam for an exposure period of 3-15 seconds.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method having application
in the field of medicine and, more particularly, in the field of
surgery involving a laser radiation source operable to form a
surgical suture.
[0002] White R. A. et, Mechanism Of Tissue Fusion In Argon
Laser-Welded Vein-Artery Anastomoses, Lasers Surg. Med., 1988, v.
8, pages 83-89, describes a method of joining biological tissues by
"welding" thereof with the aid of a source of laser radiation.
However, this method results in a condition at the "welded" joined
tissues in which the supply of blood thereto is not
satisfactory.
[0003] Russian Federation Application No. 96124526/14, publ. BI
No.
[0004] 6, 1999, describes a method of joining biological tissues by
treatment of the biological tissues with a laser beam so as to form
a discontinuous surgical suture. Biological tissues joined by this
method benefit from the preservation of blood flow thereto which
has a beneficial effect on the process of accretion of the joined
biological tissues. However, the noted Russian Federation
Application No. 96124526/14 does not disclose the operating
parameters of the process for forming the discontinuous surgical
suture by means of the source of laser radiation.
SUMMARY OF THE INVENTION
[0005] An object of the method of the present invention is to
provide a suitable set of operational parameters for obtaining a
quality discontinuous surgical suture by performance of the
method.
[0006] In accordance with one aspect of the method of the present
invention, the method can be performed to join biological tissues
with a plurality of discontinuous surgical sutures by treatment of
the biological tissues with a laser beam having a power flux
density of 1-7 kW/cm.sup.2, preferably 3-5 kW/cm.sup.2, on the
surface of the joined biological tissues.
[0007] In accordance with another aspect of the method of the
present invention, the source of laser radiation is a laser powered
by copper vapors for generating a laser beam at a wavelength of
0.5-0.6 microns in combination with short-focus optics.
[0008] In accordance with a further aspect of the present
invention, the source of laser radiation has a radiation power of
5-15 W, preferably 811 W, at a periodic pulse operating mode of
laser beam generation and at a focal distance of the focusing
objective of 3-7 cm and that the exposure period of the biological
tissues being treated by the laser radiation is 3-15 seconds.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic view of a joint structure formed by
laser beam treatment of biological tissues for interconnecting the
biological tissues, the joint having the configuration of a "hollow
rivet";
[0010] FIG. 2 is a plot of estimates of the power flux density for
an unfocused laser beam;
[0011] FIG. 3 is a plot of estimates of the power flux density of a
focused laser beam; and
[0012] FIG. 4 is a series of illustrations of the progressive
configuration of a welded suture as its strength is tested with the
aid of air overpressure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] Experimental studies were conducted in the Laboratory of
Cellular and Molecular Pathology of the Scientific Center of the
Moscow Medical Academy Setchenov.
[0014] The following lasers were used for the laser "welding" of
biological tissues in a medical field context:
[0015] gas CO.sub.2-lasers (.quadrature.=10.6 microns),
[0016] neodymium lasers (.quadrature.=2.94 microns, 2.06 microns,
1.32 microns, 1.06 microns, 0.53 microns),
[0017] semiconductor lasers (.quadrature.=0.81 microns),
[0018] argon lasers (.quadrature.=0.51 microns, 0.49 microns)
[0019] A measure of the usefulness of a selected laser for the
joining of biological tissues is the efficiency of the delivery of
the requisite energy into the treated area for effecting the
joining of the biological tissues. On the one hand, the wavelength
of the laser radiation should provide uniform energy distribution
on the entirety of the treated area while, on the other hand, the
amount of energy absorbed by the biological tissues should be
sufficient to effect the joining of the biological tissues. The
achievement of these two objectives is dependent in many respects
upon the power (energy) of the laser radiation delivered to the
treated area, as well as upon the space and time distribution of
the energy in the treated area.
[0020] One conclusion drawn from the thus performed studies is that
it is most advantageous to use a laser beam produced with the aid
of copper vapors to form a discontinuous surgical suture. It should
be mentioned in this context that a laser of this type had not been
earlier applied in a medical context.
[0021] The results of three experimental protocols which explored
operational parameters of the method of the present invention are
set forth below.
[0022] Experimental Protocol 1
[0023] To explore one aspect of the operational parameters of the
method of the present invention, the biological tissues of internal
organs of laboratory animals (rats) were treated with laser
radiation to effect the formation of interconnecting joints between
the treated biological tissues which have the configuration of a
"hollow rivet" (see FIG. 1).
[0024] The requisite strength and density of the laser formed
suture were ensured by the selection of an appropriate frequency of
the "hollow rivet" joints and appropriate sizing of the rings
thereadjacent formed of denatured albumen.
[0025] A relatively thin stratum of necrotized tissue formed as a
result of heating ensures the necessary mechanical strength of the
suture at the initial stage of healing. After the walls of the
"rivet" are destroyed, the strength of the tissue joint is
dependent upon the size of the zone of structural reorganization of
the albumen and the extent of the denaturation thereof.
[0026] Spectral and polarizing studies of the applicants have shown
that biological tissues have relative transmittance. Thus, laser
radiation of the visible and the near IR wavelength penetrates
relatively deeply into the biological tissues. In view of the fact
that the laser radiation propagates into the biological tissues at
a speed close to the speed of light, the laser beam and,
consequently, the optical power, is delivered into the biological
tissues practically instantaneously. Accordingly, the heating of
the biological tissues commences simultaneously throughout the
entirety of the tissue lying within the borders of the localization
of the energy of the laser radiation.
[0027] A vaporization of the biological tissues occurs in the
central zone of the laser beam, at high power flux density, and a
melting of the biological tissues occurs on the periphery of the
beam. Studies of the applicants have established that the ratio
between the thickness of the joined biological tissues and the
cross sectional size of the laser beam should be (5-7): (0.8-1.2).
Accordingly, it is believed that the distribution of the power flux
density of the laser beam in its longitudinal direction determines
the uniformity of the energy conversion efficiency in the joining
zone.
[0028] A uniform distribution of the energy conversion efficiency
along the beam should result in only minimal differences in the
mechanical stresses in the joined biological tissues. Thus, it is
believed that such a condition best ensures strong welding or
joining of the biological tissues. Apparently, a desirably strong
welded or joined condition can be effected so long as the power
flux density varies only weakly in the biological tissues within
the path of the laser beam.
[0029] From the perspective of achieving a laser joining of
biological tissues, the choice of the preferred wavelength of the
laser radiation was made by taking into account the shape of the
laser beam penetrating the biological tissues. In this regard, it
was assumed that the variation of power of the laser radiation at
its propagation in the biological tissues conforms to Bouguer's
law.
[0030] The distribution of the power flux density of the laser
radiation on the biological tissues was studied at different
wavelengths of unfocused and focused laser beams and took into
account the data obtained from the experimental study of the
optical characteristics of the biological tissues. In connection
with the study of focused laser beams, it was specified that the
diameter of the beam at the input into the focusing optics was 2
cm, that the focal distance was 5 cm, and that the cross sectional
extent of the beam in the zone of the focal beam constriction was
0.03 cm.
[0031] The power flux density in any given section of the
biological tissue P(x) was normalized relative to the power flux
density on the surface of the biological tissue Po for the
wavelengths of 0.5 microns, 0.6 microns, 0.7 microns, and 0.9
microns.
[0032] The results of the study of unfocused laser beams and
focused laser beams are shown in FIGS. 2 and 3, respectively.
[0033] As seen in the plot of the results concerning the unfocused
laser beam studies shown in FIG. 2, a laser beam radiation having a
wavelength of 0.9 microns is to be preferred. The gradient of the
power flux density along the laser beam increases in correspondence
with the decrease of the wavelength of the laser beam. The largest
gradient was observed at a laser beam wavelength of 0.5 microns.
The advantage that apparently obtains in radiating in the near IR
wavelength band is that it avoids an essential problem relating to
long focus laser beam operation. In long focus laser beam
operation, a space distribution can be formed. In this mode of
operation, the dimension of the beam in a zone of focal beam
constriction is relatively larger than that of the beam in a short
focus mode of operation. Therefore, it is necessary to increase the
exposure time or the power of the laser radiation in order to
provide optimal energy-conversion efficiency. However, increasing
the exposure time decreases the operational speed of the laser
"welding" or joining and increasing the power of the laser
radiation complicates the operating conditions of the laser
delivery device used for the joining of biological tissues.
[0034] In a short focus laser beam operation with a focused beam, a
more uniform distribution of the power flux density can be provided
at the wavelength of 0.5 microns, as can be seen in FIG. 3. The
gradient of the power flux density along the laser beam increases
in correspondence with increasing wavelength. It appears that
radiation in the visible wavelength bandwidth of 0.5-0.6 microns is
to be preferred over radiation in the near IR wavelength bandwidth.
Moreover, the advantages of this preferential wavelength bandwidth
become even more apparent when considered in light of the
possibility of providing high power densities at small power of the
laser in short focus laser beam operations.
[0035] Experimental Protocol 2
[0036] Experimental studies of different operational modes of
focusing laser radiation were carried out to determine the
geometrical characteristics of a laser beam which could perform a
biological tissue joining operation. The possibility of biological
tissue joining by a laser beam was explored in both the long focus
operational mode and the short focus operational mode.
[0037] Experiments were carried out in the long focus operational
mode at a laser radiation power of 4 W and a focal distance of the
focusing objective of 80 cm. The exposure time varied from 20
seconds to 130 seconds. The power flux density on the surface of
the biological tissue was 625 W/cm.sup.2.
[0038] A burning through of the biological tissues was observed in
all cases. Welding or joining of the biological tissues was not
observed. The area of interaction of the laser beam with the
biological tissue was characterized by a clearly defined through
hole and a peripheral zone. The internal wall and the peripheral
zone were carbonized.
[0039] Experiments were carried out in the short focus operational
mode at a laser radiation power of 10.8 W and a focal distance of
the focusing objective of 5 cm. The exposure time varied from 1.5
seconds to 30 seconds. The power flux density on the surface of the
biological tissue was 1-7 kkW/cm.sup.2. Samples were studied at the
following exposures: 2 samples--1.5 seconds; 7 samples--5 seconds;
1 sample--10 seconds; 5 samples--20 seconds; and 1 sample--30
seconds.
[0040] Burning through of the biological tissues and the welding or
joining together thereof was observed in all cases. The diameter of
the biological tissue burn through increased in correspondence with
the increase in the exposure length. In contrast to that observed
in connection with the exposure time of 20 seconds, no
carbonization of the biological tissue was observed at the exposure
times of 1.5 seconds and 5 seconds.
[0041] The following observations can be drawn in connection with
the experimental results of the studies of the long focus and short
focus laser beam operational modes. Although the energy conversion
efficiency in the long focus operational mode at the exposure time
of 20 seconds approached that of the short focus operational mode
at the exposure time of 5 seconds (12.5 kJ/cm.sup.2), "welding" or
joining of the biological tissues was observed only in the case of
the short focus operational mode. It appears that space
distribution of the power flux density of the laser beam radiation
along its direction of propagation is important for the "welding"
or joining of biological tissues.
[0042] In subsequent experiments, the exposure time of the
biological tissues treated by laser radiation varied from 5 seconds
to 15 seconds at a laser power radiation of 5-15 W. The purpose of
these experiments was to determine the range of exposure times
which yield a satisfactory welding or joining of the biological
tissues.
[0043] These subsequent experiments were carried out on 9 groups of
biological tissues differing from one another essentially in
morphological characteristics such as color, pattern of fibers, and
the presence of fatty deposits.
[0044] Steady welding or joining of the biological tissues was
observed in all cases in the range of exposure times from 5 seconds
to 15 seconds.
[0045] Experimental Protocol 3
[0046] The quality of the laser welding was estimated based upon
the results of strength testing of the weld sutures and analysis of
the biological state of the zone of the suture.
[0047] The strength of the weld joints was tested by producing an
overpressure of up to 0.1 bar in the zone of the suture. In this
regard, the tested sutures were comprised on the biological tissues
welded at laser power radiations of 5-15 W and at exposure times of
5-15 seconds. FIG. 4 shows the images of a biological tissue in the
course of strength testing thereof. In all cases, the suture
maintained its mechanical characteristics and was not
destroyed.
[0048] The strength tests thus performed confirmed the strength of
the weld joints in the range of the applied overpressures.
[0049] The exposure times were varied from 1 second to 32 seconds
in connection with the study of the biological state of the welding
zones. The laser radiation power was 5-15 W.
[0050] Portions of internal organs of rats which had previously
been placed in physiological solution were used to define the
biological state of the biological tissue after the biological
tissue had been treated by the laser beam radiation so as to form
weld sutures configured as "hollow rivets".
[0051] The laser radiation power and the exposure time were varied
in the experiments. At the laser radiation power of 8-11 W, the
exposure time was at a value of 1-15 seconds, and at the laser
radiation power of 4-6 W, the exposure time was at a value of 8-32
seconds. Disruption of the biological tissue was observed at the
laser radiation power of 8-11 W during the exposure time values of
5-10 seconds. Disruption occurred much later at the lower laser
radiation power values during the exposure time values of 30-32
seconds.
[0052] The experimental studies suggest that, to obtain a quality
discontinuous surgical suture by performance of the method of the
present invention, it is necessary to treat the biological tissues
with a laser beam having a power flux density of 1-7 kW/cm.sup.2,
preferably 3-5 kW/cm.sup.2, on the surface of the joined biological
tissues. To form a discontinuous surgical suture, it is recommended
that a laser is used which is powered by copper vapors for
generating a laser beam at a wavelength of 0.5-0.6 microns in
combination with short-focus optics. It is recommended that the
source of laser radiation has a radiation power of 5-15 W,
preferably 8-11 W, at a periodic pulse operating mode of laser beam
generation and at a focal distance of the focusing objective of 3-7
cm and that the exposure period of the biological tissues being
treated by the laser radiation is 3-15 seconds.
[0053] Thus, the method of the present invention permits one to
obtain a quality discontinuous surgical suture with the use of
laser radiation.
[0054] The specification incorporates by reference the disclosure
of Russian priority document 2000-114-847 of Jun. 13, 2000.
[0055] The present invention is, of course, in no way restricted to
the specific disclosure of the specification and drawings, but also
encompasses any modifications within the scope of the appended
claims.
* * * * *